1. Field of the Invention
The present invention relates to a light-transmissible plastic plate which shields electromagnetic waves. More particularly, the present invention relates to a light-transmissible plate capable of effectively shielding deleterious electromagnetic waves which are generated from, for example, a display or a Braun tube. Moreover, the present invention relates to a light-transmissible plate having durability and the ability to reduce reflection.
2. Description of the Prior Art
Displays of office automation equipment, for example, word processors or computers, or Braun tubes of game machines or television sets generate deleterious electromagnetic waves. There are some problems due to the electormagnetic waves, which are often pointed out, for example, problems with respect to health and noises which influence other equipment. For instance, often false signals due to noises come into a computer. Also, noises of a stereo are generated when both the stereo and a television set are operating at the same time.
Many improvements have been carried out to eliminate these problems. One of the improvements is a method of covering the equipment which generates electromagnetic waves with an electroconductive material such as a metal. For example, a cloth capable of shielding electromagnetic waves and an "Eyesaver" (the trade name of a commodity of Chori Kabushiki Kaisha, a Japanese company) are known. The cloth is constructed by adhering carbon onto a fiber with a small diameter and then weaving the fiber to form a meshed structure, and the cloth is applied on equipment which generates electromagnetic waves. "Eyesaver" is constructed of glasses and metal wire positioned between the glasses.
However, since the above methods cause a partial intercepting of the ray from a display, it becomes rather difficult for an operator of the equipment to look at the display clearly.
A method for forming an evaportion coating layer of electroconductive material on a glass base plate is also known. Such a method is disclosed, for example, in Japanese Patent Publication No. SHO 49-18447. However, when the method is applied to a plastic base plate, the base plate is liable to soften or to melt, and is liable to be injured at the surface. Therefore, the method cannot be applied for manufacturing a light-transmissible plastic plate.
Moreover, with respect to anti-reflection film technology, various forming methods and various structures thereof are disclosed. Japanese Patent Publications No. SHO 59-48702, SHO 59-78301 and SHO 59-78304 disclose a method wherein a hard coating film comprising a polyorganosilane or a hardened film comprising an epoxy resin is formed on a plastic base plate and then an anti-reflection film comprising inorganic material is coated on the above hard coating layer. Japanese Patent Publication No. SHO 56-113101 discloses a structure wherein an anti-reflection film comprising a plurality of oxide compound layers is provided on a plastic base plate. The structure has high hardness at the surface and a satisfactory anti-reflection function, but adhesion between the base plate and the film, heat resistance, shock resistance, hot water resistance and weather resistance thereof are not satisfactory. Japanese Patent Publications No. SHO 45-6193, SHO 59-48702, SHO 59-78301 and SHO 50-78304 disclose other structures including other anti-reflection films, but the adhesion between the base plate and the anti-reflection film in these structures is also unsatisfactory, and the surfaces of anti-reflection films are liable to be damaged. Moreover, the plates are liable to be damaged by water or alohol, and the structures have adhesion problems between the base plate and the film after dipping the plate into hot water and also in severe weather.
Although several conventional technologies have been described, all of these technologies have a problem in accordance with adhesion between a hard coating layer provided on a base plate and a layer of anti-reflection film provided on the hard coating layer. Therefore, the anti-reflection film tends to separate from the hard coating layer over a long period of time.